Goals consist of defining the ability of exogenous nucleotides including adenosine triphosphate to bind Fe plus 2, Fe plus 3, and Mg plus 2 and then serve as donors of these metallic cations to yersiniae cultivated in simulated intracellular environments. The effect of such chelates plus known siderophores will be determined on growth of wild type, tonB, and pst (pesticin receptor) mutants cultivated in media deficient in iron, magnesium, and trace elements. Studies showing that Yersinia pestis (but not yersinia pseudotuberculosis or Yersinia enterocolitica) is naturally defective in phenylalanyl transfer RNA-protein transferase (wyb) will be completed with the intent of correlating this defect with the known deficiencies in Y. pestis accounting for its slow growth (compared to Y. pseudotuberculosis and Y. enterocolitica) and with its ability to survive in highly iron-deficient medium (Fe plus 2 is required for maturation of phenylalanyl transfer RNA). Finally, virulence of yersiniae blocked in Fe plus 3-transport will be compared to those blocked in hemin transport or biosynthesis in order to determine the in vivo iron reservoir used by these organisms.